The present invention relates to a method for precipitating vanadium from vanadium bearing liquors and, more particularly, a method for precipitating vanadium in the tetravalent and trivalent states and recovering vanadium pentoxide.
Various commercial processes used in the petroleum industry generate by-products which contain rather high concentrations of vanadium and nickel in addition to smaller concentrations of other metals. These by-products include, for example, HDM liquor which is a by-product of the hydrodemetallization processing of heavy crudes, flexicoke from the gasification process as well as others. The HDM liquor contains up to 22 grams per liter of vanadium while flexicoke contains up to 12% vanadium. As vanadium finds use in various fields such as the preparation of ferro-alloys, as a catalyst and in the production of other products, it is highly desirable to recover high purity vanadium in the form of vanadium pentoxide from the above-noted by-products in an economical and efficient manner.
Heretofore, the recovery of vanadium from vanadium bearing liquors required oxidizing the vanadium bearing liquor such that the vanadium cation species is at its highest oxidation level, that is, its pentavalent state. After the vanadium has been oxidized in solution to its pentavalent state, it is precipitated by treating the liquor with a precipitating agent such as ammonia (NH.sub.3) or ammonium chloride (NH.sub.4 Cl) so as to adjust the pH of the solution of 2 thereby precipitating vanadium pentoxide (V.sub.2 O.sub.5) and ammonium metavanadate NH.sub.4 VO.sub.3, respectively. The ammonium metavanadate may then be washed, dried and calcined to produce a vanadium pentoxide product. A typical precipitation method is disclosed in Canadian Pat. No. 783,006. While the foregoing process has been useful in recovering vanadium, it does suffer from a number of disadvantages. The primary disadvantage is that the purity of the vanadium pentoxide product is generally below 87% V.sub.2 O.sub.5. In addition, the process tends to be inefficient in that only 90% of the vanadium in solution is precipitated.
In light of the foregoing, it would be highly desirable to provide a process for precipitating and recovering vanadium from vanadium bearing liquors, particluarly HDM liquor produced during the hydrodemetallization processing of heavy crudes, in a simple, efficient and economic manner.
Accordingly, it is the principal object of the present invention to provide a method for precipitating and recovering vanadium from vanadium bearing liquors.
It is a particular object of the present invention to provide a method for precipitating vanadium in the tetravalent and trivalent states.
It is a further object of the present invention to provide a method for precipitating vanadium in the tetravalent and trivalent states from HDM vanadium bearing liquors.
Further objects and advantages of the present invention will appear hereinbelow.